Without limiting the scope of the invention, its background is described in connection with the design and fabrication of an intravascular catheter that combines intravascular ultrasound, photoacoustic and elasticity imaging and is capable of intravascular radiation and/or acoustic therapy.
WIPO Patent Application No. WO/2010/080776 (Thornton, 2010) describes a catheter assembly for an intravascular ultrasound system that includes a catheter and an imaging core disposed in the catheter. The imaging core includes a rotatable driveshaft, at least one light source, and at least one transducer. The at least one light source is disposed at a distal end of the rotatable driveshaft. The at least one light source is configured and arranged for rotating with the driveshaft and also for transforming applied electrical signals to light for illuminating an object in proximity to the catheter. The at least one transducer is also disposed at the distal end of the rotatable driveshaft. The at least one transducer is configured and arranged for rotating with the driveshaft. The at least one transducer is configured and arranged for receiving acoustic signals generated by the object in response to illumination of the object by the light emitted from the at least one light source.
U.S. Pat. No. 7,711,413 issued to Feldman et al., (2010) relates to a catheter imaging probe for a patient. The probe of the Feldman patent includes a conduit through which energy is transmitted. The probe includes a first portion through which the conduit extends. The probe includes a second portion which rotates relative to the conduit to redirect the energy from the conduit. A method for imaging a patient. The method includes the steps of inserting a catheter into the patient. There is the step of rotating a second portion of the catheter relative to a conduit extending through a first portion of the catheter, which redirects the energy transmitted through the conduit to the patient and receives the energy reflected back to the second portion from the patient and redirects the reflected energy to the conduit.
Intravascular ultrasound (IVUS) imaging is widely used to image the atherosclerotic plaques in coronary arteries.1-3 This invasive catheter-based approach is suitable to detect unrecognized disease, lesions of uncertain severity (40% to 75% stenosis), and risk of stratification of atherosclerotic lesions in interventional practice. Histopathalogical information, obtained from the IVUS, is not enough to characterize the plaques due to poor contrast between tissue's ultrasound properties, therefore an additional modality such as intravascular photoacoustic imaging (IVPA) must be used to assess the vulnerability of the plaques.
The IVPA imaging as a part of combined IVUS/IVPA imaging that was demonstrated by Sethuraman et al.4 Photoacoustic imaging relies on contrast of light absorption constituents presented inside the arterial tissues and is based on an excitation of a tissue with shot laser pulses with consequent detection of acoustic transients, generated as a result of thermal expansion.5-7 Currently, the photoacoustic imaging is successfully used in different biomedical areas.
The intravascular elasticity imaging as a part of the described intravascular imaging is used to image a distribution of shear elastic modulus in the artery.8-11 The elasticity imaging relies on a stiffness contrast of artery tissues and plaques content and is based on obtaining several ultrasound images of the same cross-section of the artery during the deformation of the artery's wall under either externally applied force or as a result of normal cardiac cycles or a combination thereof. Using inverse problem formulations, the elasticity distribution is evaluated based on a distribution of the strain tensor components. The elasticity imaging approach is widely used in various clinical applications.12-16 
Once pathology is detected and its vulnerability is assessed, the same integrated IVUS/IVPA imaging catheter can be used for thermal and/or radiation and/or acoustic therapy of the pathology. In such therapy, the absorbed light energy or acoustic energy or both is converted into a heat leading to necrosis of the pathology tissues. While the pulsed laser is coupled with the catheter to perform diagnostics imaging, the continuous wave (CW) source of a radiation, for instance, a CW laser, should be coupled with the catheter.17-20 The laser is operated at a wavelength that is primarily absorbed by a typical pathology of the cells and molecules.
To enhance the radiation therapy effect, Shah et al. has proposed to use nanoparticles-based contrast agents.19 Such contrast agents are conjugated with antibodies and can be injected into a blood vessel. After a certain time needed for contrast agents to reach the pathology and label the specific cells, the tissue is irradiated with CW laser light. The radiation is primarily absorbed by nanoparticles which cause heating. The heated nanoparticles lead to a temperature increase in the tissue environment thus inducing therapeutic effects.
In the acoustic therapy, a relatively low-frequency, high-intensity focused ultrasound (HIFU) beam is directed in the area of the detected pathology and, due to acoustic absorption, scattering and/or reflecting, leads to a temperature increase thus resulting in necrosis of the pathology tissues.21,22 The HIFU treatment is also well-known modality of non-invasive therapy and can be performed either from outside or from the inside of the artery. However, to perform all of these imaging and therapy procedures clinically, specially designed catheters need to be used. Currently available catheters cannot be used both for combined IVUS, IVPA and elasticity imaging and for radiation and/or acoustic therapy.
The present invention describes two representative designs of fiber-based integrated catheters both for combined IVUS/IVPA imaging and for intravascular radiation and/or acoustic therapy. One design is based on single-element catheter-based ultrasound transducers coupled with specially designed light delivery systems. In this approach, the light delivery system is based on the side fire fiber, similar to that utilized for biomedical optical spectroscopy23 or on the micro-optics in a manner of a probe for optical coherent tomography. In the second design, the integrated catheter is based on ultrasound array transducer that also is coupled with the side fire fiber or micro-optics light delivery system. In both types of the integrated catheters, the light delivery systems were designed to direct the light into the area or tissues imaged by the ultrasound transducer. In addition to that, the CW radiation utilized for radiation therapy is also delivered in the same area. Finally, an intravascular acoustic therapy can be performed using one or more ultrasound units that deliver the acoustic radiation in the desired area of the artery. Tunable in wide spectral range a Ns-pulsed laser-based system was employed as a light source for photoacoustic imaging, while ultrasound pulser/receiver was used for ultrasound imaging.